Wastewater is typically treated in order to remove undesirable contents and provide an effluent that can safely be returned to the environment. Bacteria can assist in this process, particularly in respect of breaking-down ammonia that may be present in the wastewater. The biological reaction by which ammonia is removed involves the conversion, first, aerobically, of the ammonia and other nitrogen-containing compounds to nitrates through bacterial nitrification; followed by the second step in which anoxic bacterial denitrification converts the nitrates into nitrogen gas which is then separated from the wastewater.
Anoxic bacteria require an oxygen-free, or relatively oxygen-free environment in which to thrive. Accordingly, the anoxic treatment of reaction liquor is carried out in a container that minimizes the exposure of the bacteria to oxygen. This is achieved by providing a reactor in which a reaction liquor can be treated by submerging the bacteria in the reaction liquor and possibly but not necessarily by having a mechanical seal preventing the air outside the reaction liquor reactor from penetrating into the reaction liquor contained within the reactor.
In recent years, biochemical reactors have been configured to accommodate biofilms. The term “biofilm” as used herein may be defined as a layer of a biomass on a substrate. Microorganisms within a biofilm thrive and are more reactive when they are in direct contact with the liquor that supplies such bacteria with nutrients. In the context of the present invention, when used in an anoxic biological contactor, the bacteria of the anoxic type have an affinity to the carrier material of the substrate. Through use of an appropriate substrate, the bacteria maintained within the reactor and may be highly concentrated. Biodegradation within such a biochemical reactor generally proceeds on the basis of a flow of influent containing nitrites and/or nitrates over the biofilm and the rate of reaction is proportional to the quantity of bacteria exposed. In a biofilm system, as microorganisms grow on fixed surfaces of their supporting substrate, the biofilm grows in thickness as the microorganisms multiply. Eventually part of the biofilm will detach from the substrate as the bacteria lose their vitality and new biofilm will be formed in place on the substrate. The reactivity of such systems can be improved by increasing the rate at which less active and dead bacteria are sloughed-off the supporting substrate.
Past biofilm reactors have incorporated rotating biological contactor support surfaces which serve to accelerate this regeneration process. Some patents, which are directed to the use of anoxic biological contactors, include the following:    U.S. Pat. No. 6,676,836 patented Jan. 13, 2004 by M.G. Mandt;    U.S. Pat. No. 6,620,322 patented Sep. 16, 2003 by Smith & Vessio LLC;    U.S. Pat. No. 6,413,427 patented Jul. 2, 2002 by Ecokasa Inc.;    U.S. Pat. No. 5,702,604 patented Dec. 30 1997 by Yamasaki et al;
Of the many patents which relate to the above subject matter are the following:    U.S. Pat. No. 5,908,555 patented Jun. 1, 1999 by Hydrometrics Inc;    U.S. Pat. No. 5,811,259 patented Sep. 22, 1998 by EcoMat Inc;    U.S. Pat. No. 5,395,528 patented Mar. 7, 1995 by Lyonnaise des Eaux-Dumez S.A.;    U.S. Pat. No. 5,073,256 patented Dec. 17, 1991 by Norddeutsche Seekabelwerke; and    U.S. Pat. No. 4,126,545 patented Nov. 21, 1978 by Research Corporation;
Some known types of biological reactors employ backwashing of the biofilm support surfaces at regular intervals in order to remove the excess biomass that accumulates. These reactors proceed, therefore, in a discontinuous manner, constituting a disadvantage of this known process. In order to avoid the complete shutdown of the bioreactor during the frequent, necessary washing of the contactors, several contactors were sometimes provided, of which alternately one contactor is always in operation, while the other contactor was being backwashed. Apart from the necessary duplication of equipment required by this procedure, the unit in the operation experiences declining performance as caking progressively occurs within the biofilm prior to the back washed cycle.
Prior biological treatment processes also rely on circulating and recirculating the reaction liquor over the biofilm substrates. In cases where the bacteria tend to multiply rapidly a tendency may develop for the bacteria to fill-up the spaces between the biofilm substrate. This can cause an increase in the hydraulic resistance to the flow of the reaction liquor and, at times, result in the mechanical plugging of certain portions of the space between biofilm substrates. As a result, the flow of reaction liquor within the bioreactor decreases, which, in turn reduced the liquor flux across the bacteria. The overall efficiency of the contactor is thereby decreased. It is known that maintaining a thin biofilm of relatively constant thickness on the support substrate is also essential for optimal operation of such a system.
A further disadvantage of prior art contactors is that the drive systems provided by the prior art are typically substantially in contact with the corrosive reaction liquor. The “drive system” includes the basic actuator, e.g. a motor or hydraulic cylinder, and the linkages that extend between such actuator and the biological supports within the reactor. The immersion of any articulated components within the reaction liquor can expose the drive system to damage caused to the corrosive action of the reaction liquor.
The above-described constraints and problems associated with conventional bioreactors have created a need for a solution. Bearing in mind the problems and deficiencies of the prior art, it would therefore be desirable to provide an improved biological contactor.
It would also be desirable to be able to provide a media drive system that is protected from the corrosive effects the reaction liquor and is easily accessible for maintenance.
The invention in its general form will first be described, and then its implementation in terms of specific embodiments will be detailed with reference to the drawings following hereafter. These embodiments are intended to demonstrate the principle of the invention, and the manner of its implementation. The invention in its broadest sense and more specific forms will then be further described, and defined, in each of the individual claims which conclude this Specification.